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Inorganic sol-gel solutions were electrospun to produce the first bioactive three-dimensional (3-D) scaffolds for bone tissue regeneration with a structure like cotton-wool (or cotton candy). This flexible 3-D fibrous structure is ideal for packing into complex defects. It also has large inter-fiber spaces to promote vascularization, penetration of cells and transport of nutrients throughout the scaffold. The 3-D fibrous structure was obtained by electrospinning, where the applied electric field and the instabilities exert tremendous force on the spinning jet, which is required to be viscoelastic to prevent jet break up. Previously, polymer binding agents were used with inorganic solutions to produce electrospun composite two-dimensional fibermats, requiring calcination to remove the polymer. This study presents novel reaction and processing conditions for producing a viscoelastic inorganic sol-gel solution that results in fibers by the entanglement of the intermolecularly overlapped nanosilica species in the solution, eliminating the need for a binder. Three-dimensional cotton-wool-like structures were only produced when solutions containing calcium nitrate were used, suggesting that the charge of the Ca(2+) ions had a significant effect. The resulting bioactive silica fibers had a narrow diameter range of 0.5-2μm and were nanoporous. A hydroxycarbonate apatite layer was formed on the fibers within the first 12h of soaking in simulated body fluid. MC3T3-E1 preosteoblast cells cultured on the fibers showed no adverse cytotoxic effect and they were observed to attach to and spread in the material.

Bone grafts are commonly used to regenerate bone in defect sites resulting from disease or trauma but there is clinical need for artificial materials that will be readily available and reduce pain and recovery time for the patient. Current artificial bone graft materials are bioactive ceramics and glasses, which are too brittle for bone defects that experience cyclic load. The synthesis of a new nanocomposite material is described that has the potential of being a tough off-the-shelf artificial bone graft that can regenerate a bone defect and have enough flexibility to press-fit into place. The poly(γ-glutamic acid)/bioactive silica hybrid material with composition 40 wt% organic and 60 wt% bioactive inorganic (composition 70 mol% SiO 2 and 30 mol% CaO) was synthesised using a sol-gel route. The potential advantage of a hybrid material over conventional composites is the molecular scale interactions between the bioactive inorganic and the tough degradable organic. The organic and inorganic chains were covalently crosslinked using an organosilane that has an organic functionality to bond to poly(γ-glutamic acid) (γ-PGA) and an alkoxysilane group that condenses with the inorganic phase. The covalent cross-linking (class II hybrid)is required to control the dissolution and improve mechanical properties of the material. The two key variables, the concentration of cross-linking agent and the addition of calcium, were investigated by 29 Si solid-state NMR and electron microscopy. The hybrid materials were bioactive in simulated body fluid (SBF) with a hydroxy carbonate apatite (HCA) layer detected after immersion for 72 h. The hybrid material favours cell attachment and is not cytotoxic as demonstrated by culture of the osteosarcoma cell line SaOs-2 on the material for 4 days. This journal is

The need to shift from tissue replacement to tissue regeneration has led to the development of tissue engineering and in situ tissue regeneration. Both of these strategies often employ the use of scaffolds--templates that allow cells to attach and then guide the new tissue growth. There are many design criteria for an ideal scaffold. These criteria vary depending on the tissue type and location in the body. In any application of a scaffold it is vital to be able to characterise the scaffold before it goes into in vitro testing. In vitro testing allows the cell response to be investigated before its in vivo performance is assessed. A full characterisation of events in vitro and in vivo, in three dimensions (3D), is necessary if a scaffold's performance and effectiveness is to be fully quantified. This paper focuses on porous scaffolds for bone regeneration, suggests appropriate design criteria for a bone regenerating scaffold and then reviews techniques for obtaining the vitally important quantification of its pore structure. The techniques discussed will include newly developed methods of quantifying X-ray microtomography (microCT) images in 3D and for predicting the scaffolds mechanical properties and the likely paths of fluid flow (and hence potential cell migration). The complications in investigating scaffold performance in vitro are then discussed. Finally, the use of microCT for imaging scaffolds for in vivo tests is reviewed.

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Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol-gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ-glutamic acid) (γ-PGA) was introduced into the sol-gel process to produce a hybrid of γ-PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol-gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low-temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid-state NMR spectroscopy, which showed ionic cross-linking of γ-PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross-linking of γ-PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).

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Screw‐assisted material extrusion technique is developed for tissue engineering applications to produce scaffolds with well‐defined multiscale microstructural features and tailorable mechanical properties. In this study, in situ time‐resolved synchrotron diffraction is employed to probe extrusion‐based 3D printing of polycaprolactone (PCL) filaments. Time‐resolved X‐ray diffraction measurements reveals the progress of overall crystalline structural evolution of PCL during 3D printing. Particularly, in situ experimental observations provide strong evidence for the development of strong directionality of PCL crystals during the extrusion driven process. Results also show the evidence for the realization of anisotropic structural features through the melt extrusion‐based 3D printing, which is a key development toward mimicking the anisotropic properties and hierarchical structures of biological materials in nature, such as human tissues.